Method of starting a forced flow steam generator and apparatus for carrying out the method



Nov. 23, 1965 w. AUGSBURGER 3,219,018

METHOD OF STARTING A FORCED FLOW STEAM GENERATOR AND APPARATUS FOR CARRYING OUT THE METHOD Filed Jan. 16, 1965 6 Sheets-Sheet 1 l I 1 1r 1? Jnvenfor:

Nov. 23, 1965 w, AUGSBURGER 3,219,018

METHOD OF STARTING A FORCED FLOW STEAM GENERATOR AND APPARATUS FOR CARRYING OUT THE\METHOD Flled Jan 16, 1965 6 Sheets-Sheet 2 Jn van [0 r.- WALTER fluesBz/Rez-"R 1965 w. AUGSBURGER 3,219,018

METHOD OF STARTING A FORCED FLOW STEAM GENERATOR AND APPARATUS FOR CARRYING OUT THE METHOD Filed Jan. 16, 1963 6 Sheets-Sheet 3 7 7 \w Qi Q Q 0 Q Q Q N Q N INVENTOR.

BY M14 Tm AUGSBl/RGER W. AUGSBURGER G A FOR FOR CARRY Nov. 23, 1965 3,219,018 0w STEAM GENERATOR CED FL ING METHOD OF STAR'IIN AND APPARATUS Filed Jan. 16, 1963 OUT THE METHOD 6 Sheets-Sheet 4 @Nh mi MUM/70655 (mam Nov. 23, 1965 w. AUGSBURGER 3,219,018 METHOD OF STARTING A FORCED FLOW sTEAM GENERATOR AND APPARATUS FOR CARRYING OUT THE METHOD Filed Jan. 16, 1963 6 Sheets-Sheet 5 w iiii lli Fly. 6

3,219,018 TOR Nov. 23, 1965 w. AUGSBURGER METHOD OF STARTING A FORCED FLOW STEAM GENERA TUS FOR CARRYING OUT THE METHOD 6 Sheets-Sheet 6 AND APPARA Filed Jan. 16, 1963 INVENTOR WALTER AUG 55 6 ATTORNEY United States Patent METHOD OF STARTING A FORCED FLOW STEAM GENERATOR AND APPARATUS FOR CARRY- ING OUT THE METHOD Walter Augsbnrger, Winterthur, Switzerland, assignor to Sulzer Freres, S.A., Winterthur, Switzerland, a corporation of Switzerland Filed Jan. 16, 1963, Ser. No. 251,901 Claims priority, applicatiog/Switzerland, Jan. 18, 1962, 59 62 7 Claims. (Cl. 122-406) The present invention relates to a method of and apparatus for starting a forced flow steam generator having a tubular heating system including at least two tubular heating sections arranged in series relation with respect to the flow of the operating medium and a conduit laterally connected to said tubular heating system downstream and upstream of a subsequent heating section downstream of the first heating section for temporarily stopping flow of operating medium through said subsequent heating section.

The object of the present invention is to provide an improved method of and apparatus for starting a forced flow steam generator after operating interruptions during which the steam generator does not cool down to the ambient temperature. With the method according to the invention the unavoidable heat loss during starting and the time required for starting are reduced. According to the invention the temperature of the operating medium at the outlet of one of the tubular heating sections and the temperature of the subsequent heating section or of the combustion gases heating the subsequent heating section are measured and flow of operating medium through the subsequent heating section is stopped until the temperature of the subsequent heating section or of the gas heating same is substantially equal to the temperature of the operating medium leaving the preceding heating section.

An advantage attained by the invention, in addition to the shortening of the starting period, is that the subsequent heating section through which flow of operating medium is stopped at the beginning of the starting period and which usually is a superheater made of a material which must be protected from temperature shock, for example austenitic steel, is guarded against damages caused by abrupt temperature changes because the invention prevents flow of operating medium through the sub sequent heating section unless the temperature of the operating medium is substantially equal to the temperature of the subsequent heating section.

According to the invention a forced flow steam generator having at least two tubular heating sections arranged in series relation with respect to the flow of the operating medium is provided with conduits for diverting operating medium from a subsequent heating section, with means for stopping the flow of operating medium through the subsequent section, with means for influencing the temperature of the operating medium leaving the preceding heating section, with means producing a signal corresponding to the temperature of the operating medium at the outlet of the preceding heating section, with means producing a signal corresponding to the temperature of the subsequent heating section, and with means for comparing the two signals and producing control signals for actuating the means for stopping the flow of operating medium through the subsequent heating section.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of embodi- "Ice ments thereof when read in connection with the accompanying drawing wherein:

FIG. 1 is a diagrammatic illustration of a plant according to the invention.

FIG. 2 is a diagrammatic illustration of a modified plant according to the invention.

FIG. 3 is a plan view of a starting device with the top cover removed, used in the plant shown in FIG. 1.

FIG. 4 is a large scale sectional view of a portion of the device shown in FIG. 3, the section being made along line IV-IV of FIG. 3.

FIG. 5 shows a section of the portion shown in FIG. 4 and made along line VV of FIG. 4.

FIGS. 6 and 7 are diagrammatic illustrations of apparatus indicated by blocks in FIG. 2.

FIG. 8 is a diagrammatic illustration of an acoustic device suitable for use in the plant according to the invention.

FIGS. 9 and 10 are diagrammatic, part-sectional illustrations of apparatus indicated by blocks in FIG. 1.

The plant:

FIG. 1 of the drawing diagrammatically illustrates a plant for generating steam at supercritical pressure. Numeral 1 designates a combustion chamber whose interior walls are lined by tubes forming a heating surface section 5 wherein a liquid operating medium is vaporized. The steam or vapor produced in the heating surface section 5 consecutively flows through tubular heating sections 10, 11 and 16 wherein the vapor or steam is superheated. The heating surface sections 10, 11 and 16 are placed in a flue 2 and in a space 3 connecting the combustion chamber 1 .to the flue 2. The heating surface 16 passed last by the vapor or steam is made of a material which is sensitive to heat shocks, for example austenitic steel, and must be protected from abrupt temperature changes particularly when starting the steam generator. Economizer heating surfaces 30 and 31 are placed in the flue 2 below the heating surface section 10. Liquid operating medium is supplied to the economizer section 30 through a feed pipe 32. The outlet of the economizer section 31 is connected to the inlet of the heating section 5. Two preheaters 33 are arranged in the feed pipe 32. A feed pump 34 supplies feedwater from a feedwater reservoir 37 to the feed pipe 32.

The heating section 16 furnishes steam through a steam 1 main 7 and a turbine inlet valve 21 to the high pressure part 8 of a turbine plant which drives an electric generator 35. A reheater 36 is interposed between the high pressure part 8 of the turbine plant and the inlet of a medium or low pressure part 9 of the turbine plant. This reheater is placed in the upper part of the combustion chamber 1. An inlet valve 22 controls the steam supply from the reheater to the low pressure turbine 9. The latter discharges steam into a condenser 38, the condensate being pumped by a pump 40 through a pipe 39 and through two steam-heated preheaters 41 into the reservoir 37.

A pipe 42 is connected to the conduit connecting the heating surface sections 5 and 10. The pipe 42 terminates in the feedwater reservoir 37, a pressure maintaining valve 6 being interposed in the pipe 42. The valve 6 is controlled by a control apparatus 44 which is actuated by a signal corresponding to the pressure p in the pipe 42 upstream of the valve 6 and sensed by a pressure sensitive device 45. The control apparatus 44 also receives a set point signal p through a conduit 46 from a starting device 25 whose front is shown in FIG. 1 and which will be described later.

A pipe 47 is connected to a conduit connecting the heating surface sections 11 and 16. The pipe 47 termi nates in a steam separator 13 and is provided with a valve 12. The latter is controlled by a control apparatus 17 in response to the temperature t of the operating medium in the pipe 47 upstream of the valve 12 which temperature is sensed by a device 15. The apparatus 17 also receives a set point signal r through a conduit 48 from the starting device 25. In addition, the apparatus 17 receives from the device 25 an upper and a lower limit signal a and a through conduits 51 and 52, respectively. A detail disclosure of an apparatus corresponding to the apparatus 17 can be found in FIG. 9 wherein like parts are designated by like numerals as in FIG. 1. The apparatus for comparing the actual temperature t with the set point signal r shown on the left side of FIG. 9 corresponds to the apparatus shown in FIG. 6. Whereas in the latter figure the servo-piston directly actuates a valve, in the device shown in FIG. 9 the servo-piston controls the fluid pressure in a hydraulic control system for actuating the valve 12.

The steam space of the separator 13 is connected by a pipe 53 provided with a valve 54 to the inlet of the reheater 36. A pipe 57 provided with a valve 58 is connected to the outlet of the reheater 36 and is connected through an injection cooler 59 to the condenser 38. The liquid space of the separator 13 is connected by a pipe 55 to the feedwater reservoir 37. The pipe 55 is provided with a valve 56 which is actuated in response to the water level in the separator 13. A bypass pipe 19 is connected to the steam main 7 and terminates in the pipe 47 downstream of the valve 12 or may be directly connected to the steam space of the separator 13. The by-pass pipe 19 is provided with a valve 20 controlled by an apparatus 60 which is responsive to the pressure p in the steam main 7 and which receives a set point signal p from the starting device 25 through a signal conduit 61.

For controlling the supply of liquid operating medium to the steam generator a temperature sensitive element 14 is connected to the conduit connecting the heating surface section to the heating surface section 10. The element 14 produces a signal corresponding to the temperature t of the operating medium leaving the heating section 5 which signal is conducted through a conduit 63 to a device 62 which receives a set point signal t from the starting device 25 through a conduit 64 and produces a signal corresponding to the difference between the actual temperature t and the desired temperature r The output of the device 62 is connected through a conduit 65 to a control apparatus 66 which controls the output of the feed pump 34 by controlling a steam turbine 32 according to the signal produced by the device 62. The control apparatus 66 receives through a conduit 67 a limit signal W from the starting device 25, corresponding to the minimal permissible rate of feedwater supply. A detail disclosure of an apparatus corresponding to the aforedescribed arrangement can be found in FIG. 10. The apparatus 62 is the same as the apparatus 62 shown in FIG. 7. As apparatus 66 a modification of the arrangement shown on the right side of FIG. 9 is used.

The combustion chamber 1 is provided with burners 68 which receive fuel from a pipe 69 controlled by a valve 70. This valve 70 is actuated by a control apparatus 71 according to control signals F received from the starting device 25 through a signal conduit 72 and corresponding to the required rate of fuel supply.

A temperature sensitive device 75 is placed adjacent to the heating surface section 16 which must be guarded against abrupt temperature changes. The device 75 is connected through a signal conduit 76 to the starting device 25. The device 75 senses the temperature of the combustion gases which heat the heating surface section 16 and produces a signal corresponding to the temperature t of the combustion gases. The temperature sensed by the device is indicated by a horizontal, linear indicator 28 movable vertically in front of a rectangular dial on the front of the device 25. The temperature t corresponds substantially to the temperature of the heating surface 16. Instead of measuring and indicating the temperature of the combustion gases which heat the section 16, the temperature sensitive device 75 may be directly connected to the heating surface 16 for measuring and indicating the temperature thereof.

The starting apparatus:

FIG. 3 is a plan view of the starting apparatus 25 with the front plate removed. Numeral designates a motor which drives through a spur gear a shaft 101 carrying eight cams. The first cam on the left side of FIG. 3 actuates an apparatus which will be described later, for producing the signal P, the second cam initiates the signal p the third cam the signal 1 the fourth cam the signal r the fifth cam the signal a the sixth cam the signal a the seventh cam the signal p and the eighth cam the signal W The motor 100 also drives a shaft 102 through a bevel gear. Each end of the shaft 102 carries a sprocket wheel 103 driving an endless chain to which a vertical, linear indicator 27 is connected and slowly moved from left to right over the rectangular dial in front of the device 25.

The apparatus 25 includes a conventional motor 104 actuated by the temperature i which is transmitted to the motor 104 by the conduit 76 (FIG. 1). The motor 104 drives a sprocket wheel 105 driving an endless chain 106. The latter drives a second endless chain 106' through shafts 107. The horizontal, linear indicator 2% is connected to the chains 1106, 106' for vertical movement over the rectangular dial in front of the device 25.

FIGS. 4 and 5 show the apparatus actuated by the first cam on the left side of FIG. 1. The apparatus actuated by the other cams are like the illustrated apparatus. The cam presses against a spring 110 and the latter against a bell-shaped piston 111 provided with a slot 114 which controls ports for admitting a pressure fluid from a conduit 112 into the interior of the piston 111 or discharging pressure fluid from the piston into a conduit 113. The interior of the piston communicates through a channel 115 with a space 117 in a cylinder wherein a control piston 116 is movable. When starting the steam generator the piston 116 is in the position shown in FIG. 5. The space 117 is connected to a channel 118 connected to the conduit 72F. Depending on the angular position of the respective cam, a pressure prevails in the piston 1 11 which is transmitted through the channels 115 and 118 into the respective signal conduit. When starting the steam generator the motor 100 is started, causing the indicator 27 to move across the dial from left to right in FIGS. 1 and 3 and to actuate the pistons 111 to effect the pressures in the signal conduits 72, 46, 64, 48, 51, 52, 61 and 67 corresponding to the signals F, p t r a a p and W The right end of the shaft 101 is provided with a cam 120 actuating through a cam follower 121 an angle lever 123. The latter actuates a rod 124 to which the control pistons 116 are connected.

The cam 1 20 is so shaped as to cause the rod 124 and of the control pistons 116 connected thereto to move to the right at the end of the starting period of the steam generator whereby the pistons 116 close the channels 115 and connect the channels 118 to channels 126. The channels 126 are individually connected to pipes 127 wherein fluid pressures prevail which correspond to signals produced by a conventional load control device for transmitting signals corresponding to the load to the individual control apparatus 71, 44, 62, 17, 60, 66. Since the invention relates only to a starting method and apparatus, the load control device does not form part of the present invention and is not illustrated. Reference is rnade to Patent No. 2,962,865.

The dial in front of the device 25 shows graphs of desired operating characteristics produced by the devices which are influenced by the signals produced in the device 25, the graphs showing the minimal temperature a and the maximal temperature a of the operating medium leaving the heating section 11, the minimal permissible rate of feedwater supply W the rate of fuel supply F, the set point r of the means controlling the temperature of the operating medium leaving the section 11, the set point p of the means controlling the pressure of the medium leaving the steam generator, the set point t of the apparatus for controlling the feedwater supply, and the set point p for controlling the pressure of the operating medium leaving the section 5.

The dial shows a dotted line indicating the temperature of the heating section 16 if the starting operation proceeds in an orderly manner. If this is the case the point of intersection of the indicators 27 and 28 moves at or close to the dotted line and the operator Watching the dial can notice immediately if, for some reason, the timing of the increase of the temperature i is not normal.

Operation: During normal operation the valves 6, '12, 20, 54 and 58 are closed and the turbine inlet valves 21 and 22 are open. The feed pump 34 supplies liquid operating medium through the feed pipe 32 whereby the rate of supply is controlled by the control device 62 in response to the temperature 23 The operating medium passes consecutively through the economizers 30 and 31 and the heating surface 5 wherein the operating medium is vaporized. The vapor passes through the superheating surfaces 10, 11 and 16 and therefrom through the main 7 into the high pressure part 8 of the turbine plant. After partial expansion in the high pressure turbine the vapor flows through the reheater 36 and thereupon through the low pressure part 9 of the turbine plant. The exhaust of the latter is condensed in the condenser 38 and re turned by the pump 40 to the reservoir 37.

When the plant is taken out of service the rate of fuel supply and the output of the turbine are reduced to about 30% of the normal load whereupon the valve 21 is closed.

This causes an increase of pressure downstream of the superheater 16 so that the by-pass valve 20 is opened and steam flows into the separator 13. Thereupon the fuel supply is stopped and somewhat later the valve 20 is closed whereas the valves 12 and 6 are opened and liquid operating medium is circulated for a short period of time through the heating surfaces 30, 31, 5, 10 and 11.

In some cases this circulation of liquid may be omitted and the by-pass valve 20 somewhat opened in order to permit escape of vapor or steam.

When the steam generating plant is restarted, after an interruption of steam generation for several hours and when the plant is still warm, the following takes place: Air is blown for several minutes through the combustion chamber 1 and the flue 2 in order to avoid the danger of explosion of combustible gases which may still be present in the combustion chamber or in the flue. The still hot combustion chamber is thereby somewhat cooled. Parts of the steam generator located downstream of the combustion chamber, however, are not cooled and their temperature may even increase during this time. The temperature t at the device 75 remains substantially constant as shown by the left portion of the dotted line t on the dial of the device 25. The valves 20, 21 and 22 are closed and the valves 6, 12, 54 and 58 are opened. After blowing air through the combustion chamber and the flue the feedwater supply is started (time I on the dial of device 25) and a minimal rate of feedwater supply W of about 20% to 30% of the full load is effected by the feed pump 34. The liquid operating medium flows through the preheaters 33, the economizers 30 and 31 and the heating surface 5. At the connection of the pipe 42 the flow of operating medium is divided into a major portion which is returned through the pipe 42 into the reservoir 37 and into a minor portion which flows through the heating surfaces 10 and 11 and the pipe 47 into the separator 13. This minor portion flows from the separator 13 also back into the reservoir 37. During this circulation of operating medium at a small rate the temperature sensitive devices 14 and 15 merely indicate temperature but do not have a controlling effect, because the control of the feed pump 34 and of the valve 12 is also subject to the signals W and a arriving through the signal conduits 67 and 52, respectively, from the device 25. During the circulating period the operating medium cannot flow from the superheater 11 into the superhea-ter 16, because the by-pass valve 20 and the turbine inlet valve 21 are closed.

At the moment II the fire is lighted and adjusted to a minimum so that the liquid in the heating surface section 5 is warmed. The temperature of the heating surfaces 10 and 11 is slowly raised by gradual increase of the set point signal t which is conducted from the device 25 through the conduit 48 to the control apparatus 17 (time III). This changes the rate of flow of operating medium through the valve 12 which is controlled in response to the temperature sensed by the element 15. If the temperature t drops, the valve 12 is operated in closing direction and vice versa. The expansion of the operating medium in the valve 12 is accompanied by partial evaporation. Vapor and liquid are separated in the separator 13. The water flows to the reservoir 37 and the steam flows through pipe 53 and through the reheater 36, cooling the latter, whereupon the steam is conducted through the pipe 57 and the injection cooler 59 into the condenser 38.

During heating up of the heating surfaces 10 and 11 the heating surface 16 through which no operating medium passes at this time is also heated and assumes the temperature of the combustion gases passing over the heating surface 16 which temperature is sensed by the device 75. When the temperature t sensed by the element 15 is about the same or only slightly different from the temperature t sensed by the element 75, the set point signal p which is supplied through conduit 46 from the device 25 is increased to the pressure 2 which is maintained by the valve 6. This situation happens at the time IV. At this time the curve r and the indicators 27 and 28 of the device 25 intersect at the same point. The by-pass valve 20 begins to open and the valve 6 begins to close when the pressure in the tubular heating system exceeds the set point value p of the bypass valve 20 and operating medium begins to flow through the heating surface 16 without causing temperature shocks in this heating surface, because the temperature of the operating medium is substantially equal to that of the heating surface.

When the by-pass valve 20 operates as an overflow valve to maintain the pressure p and the valve 6 is closed, the valve 12 is also closed by reducing the upper limit signal a to Zero, at the time V.

As the starting operation continues the rate of fuel supply is increased at the time VI whereas the rate of feedwater supply is maintained so that the temperature t rises. Thereafter the rate of fuel supply is gradually increased in the conventional manner. This is followed by an increase of the rate of feedwater supply due to the action of the control device 62, until the desired live steam temperature is obtained and the by-pass valve 20 and the valves 54 and 58 can be closed and the turbine inlet valves 21 and 22 can be opened.

In the embodiment of the invention diagrammatically illustrated in FIG. 2 the steam generating tube system is subdivided into three heating surfaces 4, 9 and 16 which are arranged in series relation. The heating surface 4 operates as economizer and evaporator, the heating surface 9 operates as preliminary superheater and the heating surface 16 operates as final superheater. No operating medium flows through this final superheater during starting of the steam generator. The starting device is designed to also act as load control device 78 which remains operative also during normal operation when steam is supplied to a turbine plant, not shown. The device 78, which is conventional, includes a dial and a hand wheel with a pointer placed in front thereof. The hand wheel 78 may be turned from a zero position into two starting positions A A six load positions 1 to 6 and a shutting down position Z for producing signals which are conducted through conduits 46, 48, 61, 64 and 72 to control devices 44, 17, 60, 62 and 71 respectively, which correspond to the control devices designated by like numerals in FIG. 1. In contradistinction to the arrangement shown in FIG. 1 the valve 6 of the arrangement shown in FIG. 2 which is interposed in the pipe 42 connected to the conduit connecting the heating surfaces 4 and 9 and termimating in the feedwater reservoir 37 is operated in response to the temperature t at the outlet of the heating surface 9 and a valve 12' interposed in the pipe 47 connected to the conduit connecting the heating surfaces 9 and 16 is operated in response to the pressure 2 in said last mentioned conduit. The temperature t is sensed by a device 15 which produces a corresponding signal which is supplied to the control apparatus 17 actuating the valve 6. The pressure p is sensed by a device 45 which produces a corresponding signal which is conducted to the control apparatus 44 actuating the valve 12'. The pipe 47 is connected to the separator 13, valve 47' being open and valve 47" being closed, if a reheater is provided to the outlet of which the separator 13 is connected by means of a pipe 53. If there is no reheater, the pipe 47 is connected to the reservoir 37 and the pipe 53 is connected to the condenser 38, the valve 47" being open and the valve 47 being closed. For controlling the temperature of the steam emerging from the heating surface section 16 an injection conduit 80 provided with a throttle valve 81 is connected in the conventional manner to the inlet of the section 16 and to feed pipe 32, the valve 81 being controlled by an apparatus 82 which is responsive to signals produced in a temperature sensitive device 83 and corresponding to the live steam temperature t FIG. 6 is a detailed illustration of the apparatus 17 and 44 shown in FIG. 2. This illustration is self-explanatory.

FIG. 7 is a detailed illustration of the apparatus 62 and 66 shown in FIG. 2. This illustration is also self-explanatory. The feed pump 34 is driven by an auxiliary turbine 32 whose steam inlet valve is actuated by the difference Ap between the pressures downstream and up stream of a valve in the feed pipe 32 which valve is controlled by the apparatus 66.

The starting operation of the plant shown in FIG. 2 is fundamentally the same as that of the plant shown in FIG. 1. The hand wheel 79 is, if desired stepwisely, turned into the position A causing a minimal rate of feedwater flow through the heating section 4, a portion of the liquid operating medium flowing through the section 4 circulating also through the heating section 9. Thereupon supply of fuel is started and the operating medium is heated. When the temperature t is substantially equal to the temperature t a signal is produced which may be a light signal or an acoustic signal, telling the operator that the hand wheel 79 can now be turned into the position A and flow of operating medium through the heating surface 16 can be permitted.

In plants which must be restarted frequently, the signal permitting flow of operating medium through the last superheater may be given after predetermined periods of time, because in such plants it is known by experience when the temperature t at the outlet of the preceding heating surface is substantially equal to the temperature t of the subsequent heating surface.

Instead of influencing the temperature of the operating medium by changing the rate of flow thereof by varying the amount of operating medium returned to the reservoir 37, the temperature can also be influenced by injection of additional operating medium into the evaporating section, or by changing the heat supply, for example, by providing tilting burners.

A device for producing the acoustic signal is shown in FIG. 8. The conduit 76 conducting a pressure signal corresponding to the temperature t is connected through a conduit to a diaphragm chamber 151 and the conduit 48 conducting a pressure signal corresponding to the temperature 1 is likewise connected through a conduit 152 to the diaphragm chamber. The diaphragm of this chamber 151 has a rod 153 which is connected to a switch lever 154 of an electrical circuit. To this circuit belongs a bell 155 which is giving the acoustic signal if the pressures in the conduits 150 and 152 are equal, as the switch lever 154 is closing the circuit.

The temperature sensitive devices 14, 15 and 83 and the pressure sensitive devices 45 and 60' are provided with indicating instruments, which are disposed in the control room near the starting apparatus 25 and 78 respectively.

I claim:

1. A method of starting a forced flow steam generator having means for producing hot combustion gas, and a tubular heating system conducting an operating medium and including at least two heating sections in heat exchange relation with the combustion gas and arranged in series relation with respect to the flow of operating medium, the method including:

stopping flow of operating medium through the last heating section and maintaining a predetermined pressure in said tubular heating system, diverting operating medium from said tubular heating system downstream and upstream of the heating section preceding the last heating section in response to the pressure and the temperature of the operating medium leaving the preceding heating section,

sensing a temperature substantially corresponding to the temperature of the last heating section, and

permitting flow of the operating medium through said last heating section when the temperature of the operating medium leaving the preceding heating section is substantially equal to said temperature corresponding to the temperature of the last heating section.

2. A method as defined in claim 1 wherein:

operating medium is diverted from said tubular heating system at each end of said preceding heating section,

the diversion at one end of said preceding heating section being regulated in response to the temperature of the operating medium leaving said preceding heating section, and

the diversion at the second end of said preceding heating section being regulated in response to the pressure of the operating medium leaving the preceding heating section.

3. A method as defined in claim 1 wherein operating medium is diverted from said tubular heating system upstream of said preceding heating section in response to the temperature of the operating medium leaving said preceding heating section, and operating medium is diverted from said tubular heating system downstream of said preceding heating section in response to the pressure of the operating medium downstream of said preceding heating section.

4. A forced flow steam generator comprising:

means for producing a hot combustion gas at a substantially constant rate during heating up of the steam generator,

means for supplying a liquid operating medium at a substantially constant rate to the steam generator during heating up of the steam generator,

a tubular heating system connected to said supply means and including at least two heating sections arranged in series relation with respect to the flow of operating medium therethrough and in heat exchange relation with the combustion gas,

conduit means connected to said heating system downstream and upstream of a subsequent of said heating sections and including means capable of stopping the flow of operating medium through said subsequent heating section during starting and heating up of the steam generator and capable of maintaining a predetermined pressure in said subsequent heating section,

temperature influencing means connected to the heating section preceding said subsequent heating section for influencing the temperature of the operating medium flowing through said preceding section,

means responsive to predetermined, during heating up of the generator, gradually increasing temperatures of the operating medium at the outlet of said preceding heating section and operatively connected to said temperature influencing means for gradually increasing the temperature of the operating medium leaving said preceding heating section, and

means operatively connected to said subsequent heating section for sensing a temperature substantially corresponding to the temperature of said subsequent heating section,

said means capable of stopping medium flow through said subsequent heating section being also capable of allowing flow of operating medium through said subsequent heating section when the temperature of the operating medium leaving said preceding heating section is substantially equal to said temperature substantially corresponding to the temperature of said subsequent heating section.

5. A forced flow steam generator as defined in claim 4 wherein said means sensing a temperature substantially corresponding to the temperature of said subsequent heating section is placed in the combustion gas stream adjacent to said subsequent heating section for sensing the temperature of the combustion gas which is substantially equal to the temperature of said subsequent heating section.

6. A forced flow steam generator comprising:

means for producing a hot combustion gas at a substantially constant rate during heating up of the steam generator,

means for supplying a liquid operating medium at a substantially constant rate to the steam generator during heating up of the steam generator,

a tubular heating system connected to said supply means and including at least two heating sections arranged in series relation with respect to the flow of operating medium therethrough and in heat exchange relation with the combustion gas,

conduit means connected to said heating system downstream and upstream of :a subsequent of said heating sections and including means capable of stopping the flow of operating medium through said subsequent heating section during starting and heating up of the steam generator and capable of maintaining a predetermined pressure in said subsequent heating section,

means for controlling the rate of flow of operating medium through the heating section preceding said subsequent heating section for influencing the temperature of the operating medium leaving said preceding heating section,

means responsive to predetermined, during heating up of the steam generator, gradually increasing temperatures of the operating medium leaving said preceding section,

said temperature responsive means being operatively connected to said flow rate control means for gradually reducing the rate of flow of operating medium through said preceding section and for thereby gradually increasing the temperature of the operating medium leaving said preceding heating section, and

means operatively connected to said subsequent heating section for sensing a temperature substantially corresponding to the temperature of said subsequent heating section,

said means capable of stopping medium flow through said subsequent heating section being also capable of allowing flow of operating medium through said subsequent heating section when the temperature of the operating medium leaving said preceding heating section is substantially equal to said temperature substantially corresponding to the temperature of said subsequent heating section.

7. A forced flow steam generator as defined in claim 6 wherein said flow rate controlling means includes:

:a pipe laterally connected to the outlet of said preceding heating section for diverting flow of operating medium from said tubular heating system,

a pipe laterally connected to the inlet of said preceding heating section for diverting flow of operating medium therefrom,

a valve in each of said pipes,

one of said valves being operatively connected to said means responsive to the temperatures of the operating medium leaving said preceding heating section for opening said valve when the temperature rises above the predetermined temperatures and vice versa, and

means responsive to the pressure in said tubular heating system and connected to the second of said valves for opening said second valve upon increase of said pressure above a predetermined value, and vice versa.

References Cited by the Examiner UNITED STATES PATENTS 3,102,513 9/1963 Profos 122-406 PERCY L. PATRICK, Primary Examiner.

KENNETH W. SPRAGUE, Examiner. 

1. A METHOD OF STARTING A FORCED FLOW STEAM GENERATOR HAVING MEANS FOR PRODUCING HOT COMBINATION GAS, AND A TUBULAR HEATING SYSTEM CONDUCTING AN OPERATING MEDIUM AND INCLUDING AT LEAST TWO HEATING SECTIONS IN HEAT EXCHANGE RELATION WITH THE COMBUSTION GAS AND ARRANGED IN SERIES RELATION WITH RESPECT TO THE FLOW OF OPERATING MEDIUM, THE METHOD INCLUDING: STOPPING FLOW OF OPERATING MEDIUM THROUGH THE LAST HEATING SECTION AND MAINTAINING A PREDETERMINED PRESSURE IN SAID TUBULAR HEATING SYSTEM, DIVERTING OPERATING MEDIUM FROM SAID TUBULAR HEATING SYSTEM DOWNSTREAM AND UPSTREAM OF THE HEATING SECTION PRECEDING THE LAST HEATING SECTION IN RESPONSE TO THE PRESSURE AND THE TEMPERATURE OF THE OPERATING MEDIUM LEAVING THE TEMPERATURE OF THE OPERATING SENSING A TEMPERATURE SUBSTANTIALLY CORRESPONDING TO THE TEMPERATURE OF THE LAST HEATING SECTION, AND PERMITTING FLOW OF THE OPERATING MEDIUM THROUGH SAID LAST HEATING SECTION WHEN THE TEMPERATURE OF THE OPERATING MEDIUM LEAVING THE PRECEDING HEATING SECTION IS SUBSTANTIALLY EQUAL TO SAID TEMPERATURE CORRESPONDING TO THE TEMPERATURE OF THE LAST HEATING SECTION. 